1. Field of the Invention
The application relates to a method utilized in a wireless communication system, and more particularly, to a method of handling random access procedure associated to cell deactivation in a wireless communication system.
2. Description of the Prior Art
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced system is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced system targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-Advanced system for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and transmitting. In carrier aggregation, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information, and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as a primary cell (PCell). In the downlink, the component carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). In addition, cells other than the PCell are named secondary cell (SCell).
Note that, the PCell (i.e. the UL and DL PCC) is always activated, whereas the SCell may be activated or deactivated according to specific conditions (e.g. an amount of data for transmission). When a SCell is deactivated, the UE shall not monitor the physical downlink control channel (PDCCH) of the SCell and shall not receive any downlink assignments or uplink grants associated to the SCell. Besides, the UE shall not transmit on UL-SCH on the SCell and not transmit SRS on the SCell. In addition, the network activates and deactivates the SCell by sending the Activation/Deactivation command. The UE starts a deactivation timer for the SCell when the SCell is activated, wherein the SCell is deactivated when the deactivation timer expires.
According to the prior art, it is possible to configure a UE of a PCell and one SCell or more SCells. Therefore, multiple timing alignments, each for synchronization with a serving base station on uplink timing for preventing signals transmitted from the UE from colliding with those sent from other UEs under the coverage of the base station, are needed for PCell and SCell or more SCells. Note that, serving cells having uplink to which the same timing alignment applies are grouped in a timing alignment group (TAG). Each timing alignment group contains at least one serving cell with configured UL, and the mapping of each serving cell to a timing alignment group is configured by the serving eNB. To obtain initial UL time alignment for a SCell not group together with the PCell, a random access (RA) procedure is used. When the RA procedure on the SCell is performed, the UE needs to monitor PDCCH to receive message 2 of the RA procedure (i.e. random access response) and/or message 4 (i.e. contention resolution).
However, there is no guideline of how to handle the RA procedure if the SCell is deactivated during the RA procedure. For example, if a SCell is deactivated, the UE may not monitor the PDCCH on the SCell or for the SCell. According to the current 3GPP specification, the UE may perform power ramping, and retransmits message 1 (i.e. random access preamble) again and again.